Forming carrier aggregation timing advance groups in a heterogeneous network

ABSTRACT

An eNodeB operable to maintain timing advance groups (TAGs) in a heterogeneous network (HetNet) is disclosed. The eNodeB can form a timing advance group (TAG) for one or more serving cells when a same timing advance applies to the one or more serving cells. The eNodeB can map each of the one or more serving cells to the TAG using radio resource control (RRC) signaling from the eNodeB. The eNodeB can assign a timing advance group identifier (TAG ID) to the one or more serving cells mapped to the TAG. A separate timing advance timer can be maintained at a user equipment (UE) for each TAG for a selected period of time.

CLAIM OF PRIORITY

This application is a Continuation of U.S. patent application Ser. No.13/994,111, filed Apr. 14, 2014, which claims the benefit of U.S.Provisional Patent Application Ser. No. 61/523,080 filed on Aug. 12,2011, each of which are incorporated by reference in their entirety.

BACKGROUND

As the use of mobile wireless devices, such as smart phones and tabletdevices, becomes more ubiquitous, the demands on the limited amount ofradio frequency spectrum used by those devices also increases, resultingin wireless network congestion in the licensed spectrum. In addition,the increased use of high bandwidth applications such as audio and videostreaming can increase demands beyond the capability of the availablespectrum. This is especially true in high density and high use locationssuch as large cities and universities. One projection estimates a growthof 20 times in mobile internet traffic from 2010 to 2015.

One way of increasing bandwidth in wireless devices is through the useof heterogeneous wireless networks (HetNet), in which multiple nodes areco-located to provide increased data throughput to mobile devicescommunicating with one or more nodes within a cell. A cell is typicallydefined as the geographic area over which a macro base station, such asan enhanced Node B (eNode B) is configured to communicate with a mobiledevice. A macro base station can be one node located within the cell.Additional low power nodes can also be located in a cell.

A cell is often depicted as a circular area with a predefined radius.However, the actual shape of radiation patterns for antennas in a basestation can differ from the predefined radius. Moreover, the use of beamforming and/or Multiple-Input Multiple-Output (MIMO) systems enables acell to communicate at distances greater than a typical predefinedradius in certain instances. The actual radiation pattern of a basestation antenna can result in areas within the cell that have relativelylow signal strength which can result in slow data connections anddropped phone calls.

Low power nodes in the HetNet can be used to provide access to mobiledevices located in areas having low signal strength. In addition, lowpower nodes can also be used to increase the density of mobile devicecommunication in a defined area.

However, transmitting and receiving over different paths can create anumber of challenges. For example, signals communicated from mobiledevices may travel different paths between the wireless device and thenodes located within a cell. The distinct propagation paths betweendifferent carriers can create timing differences in the reception of thesignals. This can be disadvantageous in wireless systems that combinedata for multiple devices in a single signal, such as in systems thatuse Orthogonal Frequency Division Multiple Access (OFDMA).

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the invention will be apparent from thedetailed description which follows, taken in conjunction with theaccompanying drawings, which together illustrate, by way of example,features of the invention; and, wherein:

FIG. 1a is a block diagram illustrating multiple contiguous componentcarriers in accordance with an example;

FIG. 1b is a block diagram illustrating multiple non-contiguouscomponent carriers in accordance with an example;

FIG. 2 is a block diagram illustrating a communication system usingfrequency selective repeaters in accordance with an example;

FIG. 3 is a block diagram illustrating a communication system usingfrequency selective remote radio heads in accordance with an example;

FIG. 4 is a block diagram illustrating a communication system usingmultiple Coordinated Multipoint (CoMP) base stations in accordance withan example;

FIGS. 5a and 5b are block diagrams illustrating carrier aggregationserving cells assigned to timing advance groups in accordance with twoexamples;

FIG. 6 is a block diagram illustrating carrier aggregation serving cellshaving a plurality of communication nodes to form a heterogeneousnetwork in accordance with an example;

FIGS. 7a and 7b are block diagrams illustrating two examples of timingto perform a random access channel (RACH) procedure at a secondary cell(SCell) to obtain a timing advance value;

FIG. 8 is a flowchart depicting a process for forming carrieraggregation timing advance groups in a heterogeneous network (HetNet) inaccordance with an example; and

FIG. 9 illustrates a block diagram of a mobile communication device inaccordance with an example.

Reference will now be made to the exemplary embodiments illustrated, andspecific language will be used herein to describe the same. It willnevertheless be understood that no limitation of the scope of theinvention is thereby intended.

DETAILED DESCRIPTION

Before the present invention is disclosed and described, it is to beunderstood that this invention is not limited to the particularstructures, process steps, or materials disclosed herein, but isextended to equivalents thereof as would be recognized by thoseordinarily skilled in the relevant arts. It should also be understoodthat terminology employed herein is used for the purpose of describingparticular embodiments only and is not intended to be limiting.

DEFINITIONS

As used herein, the term “substantially” refers to the complete ornearly complete extent or degree of an action, characteristic, property,state, structure, item, or result. For example, an object that is“substantially” enclosed would mean that the object is either completelyenclosed or nearly completely enclosed. The exact allowable degree ofdeviation from absolute completeness may in some cases depend on thespecific context. However, generally speaking the nearness of completionwill be so as to have the same overall result as if absolute and totalcompletion were obtained. The use of “substantially” is equallyapplicable when used in a negative connotation to refer to the completeor near complete lack of an action, characteristic, property, state,structure, item, or result.

EXAMPLE EMBODIMENTS

An initial overview of technology embodiments is provided below and thenspecific technology embodiments are described in further detail later.This initial summary is intended to aid readers in understanding thetechnology more quickly but is not intended to identify key features oressential features of the technology nor is it intended to limit thescope of the claimed subject matter.

An exponential increase in the amount of wireless data transmission hascreated congestion in wireless networks using licensed spectrum toprovide wireless communication services for wireless devices such assmart phones and tablet devices, to name a few. The congestion isespecially apparent in high density and high use locations such as urbanlocations and universities.

One technique for providing additional bandwidth capacity to wirelessdevices is through the use of heterogeneous networks comprised ofmultiple communication nodes located within a cell. A communicationnode, as used herein, is defined as a base station configured to providewireless communication for one or more wireless devices located within acell. A base station may be a macro node designed to provide wirelesscommunication for devices over a relatively large area or a low powernode designed to provide wireless communication over a smaller definedarea relative to the macro node.

As previously discussed, a cell is defined as a selected geographic areaover which a macro base station, such as an enhanced Node B (eNode B) isconfigured to communicate with a mobile device. A macro base station canbe one communication node located within the cell. The macro basestation may be configured to operate based on the third generationpartnership project long term evolution (3GPP LTE) standard, includingRelease 8, Release 9, and Release 10. The 3GPP LTE base station istypically referred to as an enhanced Node B (eNode B). The macro basestation may also be configured to operate based on other standards, suchas the Worldwide Interoperability for Microwave Access (WiMAX) based onthe Institute of Electronics and Electrical Engineers (IEEE) 802.16e2005 standard and the IEEE 802.16m 2009 standard.

Low power nodes can also be located in the cell to provide coverage inareas where the macro node does not provide a desired signal strengthlevel for wireless communication. In addition, the low power nodes canbe used to provide connections for additional mobile devices in highdensity areas of the cell. Low power nodes are defined as a wirelessbase station having less output power than the macro node. Low powernodes can include micro nodes, pico nodes, femto nodes, home eNode Bs(HeNode B), remote radio heads (RRH), remote radio units (RRU),repeaters, frequency selective repeaters, and the like.

Another way of increasing bandwidth in a cell is through the use ofcarrier aggregation. Carrier aggregation enables multiple carriersignals to be simultaneously communicated between a user's wirelessdevice and a base station. Multiple different carriers can be used. Insome instances, the carriers may be from different permitted frequencydomains. This provides a broader choice to the wireless devices,enabling more bandwidth to be obtained. The greater bandwidth can beused to communicate bandwidth intensive operations, such as streamingvideo or communicating large data files.

FIG. 1a illustrates an example of carrier aggregation of continuouscarriers. In the example, three carriers are contiguously located alonga frequency band. Each carrier can be referred to as a componentcarrier. In a continuous type of system, the component carriers arelocated adjacent one another and are typically located within a singlefrequency band. A frequency band is a selected frequency range in theelectromagnetic spectrum. Selected frequency bands are designated foruse with wireless communications such as wireless telephony. Certainfrequency bands are owned or leased by a wireless service provider. Eachadjacent component carrier may have the same bandwidth, or differentbandwidths. A bandwidth is a selected portion of the frequency band.Wireless telephony has traditionally been conducted within a singlefrequency band.

FIG. 1b illustrates an example of carrier aggregation of non-continuouscomponent carriers. The non-continuous component carriers may beseparated along the frequency range. Each component carrier may even belocated in different frequency bands. The ability to use componentcarriers in different frequency bands enables more efficient use ofavailable bandwidth and increases the aggregated data throughput.

At a wireless device, such as a User Equipment (UE), the device can beconfigured to communicate with a base station (eNodeB) via a selectedcarrier. This selected carrier can be designated as a first componentcarrier. Each component carrier at the UE can appear as a serving cellat the UE, as defined by the Third Generation Partnership Project (3GPP)Long Term Evolution (LTE) Release 8 specification. The serving cellassociated with the component carrier that is configured with the fullcontrol channels/signals by the eNodeB to the UE can be referred to as aPrimary Serving Cell (PCell). The primary cell is typically the firstcomponent carrier set up for a UE. However, any component carrier can bedesignated as the PCell. If additional component carriers are needed atthe UE to provide a desired bandwidth, quality of service, or otherdesired feature, additional component carriers can be assigned to the UEby the eNodeB via the radio resource control (RRC) signaling. Eachadditional component carrier can be configured and associated with aSecondary Serving Cell (SCell) at the UE. In one embodiment, thesecondary serving cell can have no physical uplink control channel(PUCCH) transmission to the UE based on the current LTE Rel-8/9/10specifications. It should be noted that the terms “PCell and SCell” aredifferent from the generic “cell” that was previously defined. The PCelland SCell do not refer to a geographic area over which a node cancommunicate. Rather, a PCell and SCell represent a communication linkformed between a mobile device such as a UE and a node such as a macronode or a low power node.

When a UE is turned on, or activated, the distance between the UE andthe eNodeB causes a propagation delay in the signal. To account for thepropagation delay, the transmit timing at the UE can be adjusted. Thisis typically accomplished by transmitting a signal from the UE to theeNodeB and receiving a response from the eNodeB that instructs the UEhow much the transmit timing at the UE needs to be adjusted (forwards orbackwards) based on how closely the signal from the UE correlates with atiming advance signal at the eNodeB.

In the 3GPP LTE specification Releases 8, 9, and 10 designate that thesignal transmitted from the UE includes a random access preamble. Therandom access preamble can be assigned at the Medium Access Control(MAC) layer in the uplink and communicated on a Random Access Channel(RACH) such as the Physical Random Access Channel (PRACH). This signaltransmitted by the UE is received at the eNode B and correlated with atiming reference signal. A determination is made by the eNodeB how muchthe timing advance of the transmission of the carrier signal at the UEwill need to be adjusted. The timing advance may be adjusted in apositive or negative direction.

The eNodeB can then send a Random Access Response (RAR). The LTEspecification indicates that the RAR should includes an initial 11-bittiming advance, as defined in Section 6.2.3 of TS 36.321 v.10.2. The UEcan then adjust the timing of its transmissions based on the numberreceived (between 0 and 1024). The UE timing is to be adjusted with arelative accuracy better than or equal to +/−4 Ts, whereTs=1/(15,000*2048) seconds. The change in transmission timing at the UEis referred to as a timing advance (TA) adjustment. After the initialsynchronization from the RACH, the eNodeB can use other uplink signalssuch as the cyclic prefix or the uplink reference signal forsynchronization tracking and/or updating.

Currently, in the 3GPP LTE Release 10 specification, only one timingadvance value is supported with the following two restrictions for theUE configured with the carrier aggregations: (1) the timing advance isbased on synchronization to the PCell, and (2) no RACH procedure isallowed on the SCell.

The use of multiple nodes in a HetNet or multiple carrier components ofdifferent frequency bands can add additional complications in setting upa downlink and uplink connection between a wireless device and an eNodeB or other type of communication node. In 3GPP LTE Releases 8, 9, and10, when a UE is turned on and configured with the carrier aggregations,the initial random access for uplink carrier aggregation is initiatedfrom the uplink PCell only. Both the uplink PCell and SCell(s) share thesame single timing advance (TA), which is maintained on the PCell.Therefore, only one single timing advance in the uplink is supported,even when multiple component carriers in the same band or differentfrequency bands are aggregated.

There are several scenarios where separate timing advance adjustmentsper component carrier may be used to significantly increase theefficiency of carrier aggregation using multiple component carriers.Three different scenarios are illustrated in FIGS. 2-4 that may causedifferent component carriers to travel significantly differentpropagation paths and cause different propagation delays. The receptionand decoding of information carried by the component carriers can besignificantly enhanced with the use of a timing advance adjustment forone or more SCells.

FIG. 2 provides an example illustration in which a UE 202 is configuredwith a PCell associated with a first component carrier signal 206transmitted at a first frequency f₁. An SCell is associated with asecond component carrier signal 210 transmitted at a second frequencyf₂. The first component carrier signal may be relayed to the eNodeB 214by a first frequency selective repeater 218. The second componentcarrier signal may be relayed to the eNodeB by a second frequencyselective repeater 222. Each repeater 218, 222 may be positioned adifferent distance from the eNodeB 214. Depending on the location of theUE relative to each repeater and the distance of each repeater relativeto the eNodeB, the distance traveled by the first component carriersignal 206 may be substantially different than the distance traveled bythe second component carrier signal 210. If the arrival timing of thecomponent carrier signals at the eNodeB is greater than 4f_(s), then thetiming is not within the 3GPP LTE specification standard. Thus, theremay be a need to perform a timing advance adjustment for each componentcarrier.

Similarly, FIG. 3 provides an example in which a UE 302 transmits afirst component carrier signal 306 having a first frequency f₁ and asecond component carrier signal 310 having a second frequency f₂. Thefirst component carrier may be received by a first frequency selectiveremote radio head (RRH) 318 for initial baseband processing and thencommunicated to a base band unit (BBU) or eNodeB 314 for additionalprocessing and communication to a network. The second component carriermay be received by a second remote radio head 322 and communicated tothe BBU/eNodeB 314. As in FIG. 2, the position of the UE relative toeach RRH, and the position of each RRH relative to the eNodeB 314 canchange the path length of each component carrier signal and create apotential need for individual timing adjustment for each componentcarrier.

FIG. 4 provides an additional example, wherein a UE 402 is configured tocommunicate with a first eNodeB 410 and a second eNodeB 412 usingCoordinated Multipoint (CoMP) communication. The first and secondeNodeBs can be connected by a high speed optical fiber to enablecommunications between the eNodeBs to be coordinated. In this example,the UE 402 communicates via a first component carrier signal 406 havinga first frequency f₁ and a second component carrier signal 410 having asecond frequency f₂. The first component carrier can be received byeNodeB 412 and the second component carrier can be received by eNodeB414. In the context of uplink CoMP, different cells can receive the UE'ssignals on any component carrier. The timing advance could therefore bechosen to target any of the cells. Thus, different carriers could havedifferent timing advance commands. As in FIGS. 2 and 3, the position ofthe UE relative to each eNodeB can change the path length of eachcomponent carrier and create a potential need for individual timingadjustment for each component carrier.

FIG. 5a provides an example illustration of carrier aggregation (CA)serving cells. Each CA serving cell represents a connection between theUE and one or more nodes within a cell, such as a macro node and a lowpower node. As previously discussed, the primary cell is typically thefirst component carrier set up for a UE. The PCell can be designated tocarry the PUCCH for PCell communications and SCell communications.

FIG. 5a also shows two SCells, designated SCell 1 and SCell 2. The PCellmay comprise a communication between a UE and a first eNode B. SCell1may comprise a communication with a second eNode B or a low power nodeand the UE, with the second eNode B (or low power node) collocated atthe same site as the first eNode B. SCell 2 may comprise a communicationwith the UE and one or more frequency selective repeaters located at adifferent location than the first and second eNode Bs. The frequencyselective repeaters may be positioned in locations within the cell thatreceive a low power from the eNode B or that have a high volume ofwireless communication.

Since the timing advance value will be substantially similar for thePCell and SCell 1, due to the collocation of the nodes, the servingcells can be combined in a timing advance group (TA group) for which atiming advance instance is assigned. In one embodiment, the timingadvance instance may be referred to as the PCell instance. The separatelocation of the low power node in the serving cell for SCell 2 mayrequire a separate timing advance for the low power node in order forcarrier aggregation to be accomplished at the UE. Accordingly, SCell 2can be placed in a different TA group with a different timing advanceinstance that is referred to in FIG. 5a as the SCell 2 timing advanceinstance.

In one embodiment, for a TA group that includes the PCell, the referencenode can be the node associated with the PCell. For a TA group that doesnot include the PCell, the reference cell for the timing advanceinstance may be designated by the eNode B. Alternatively, the referencecell for the timing advance instance can be any active SCell in the TAgroup, as determined by the UE.

When multiple TA groups exist in a cell, an identification means isneeded to uniquely identify each TA group. The unique identification canbe used to identify a TA group in cell configurations and in the TAcommand media access control (MAC) control element (CE). A variety ofdifferent ways exist to refer to and maintain signaling with differentTA groups. For example, a cell's cell index (CI) of one of the carriercomponents in the TA group may be used to identify the TA group. Thecarrier index is already defined in the 3GPP LTE Release 10. Whenever anew carrier component is added to or removed from a TA group, thereference cell index for the TA group can be updated. In one embodiment,an implicit rule may be used, such as using the node in the serving cellin the TA group with the smallest cell index value as the reference cellfor the TA value. However, it is possible that some ambiguity may arisewhich could lead to a mismatch between an eNode B and the UE duringradio resource control (RRC) configuration when an SCell is added to orremoved from a configured TA group.

In another embodiment, a new Timing Advance (TA) index value may bedesignated for each TA group, as illustrated in FIG. 5b . In thisexample, the PCell and SCell 1 are assigned to a first TA group that isdesignated TA #1. The SCell 2, with its non-collocated low power node,is assigned to a separate TA group, designated TA#2. As previouslydiscussed, the PCell can be the reference node used to identify a timingadvance value for TA#1 since it includes the PCell. For the TA groupdesignated with a TA index value of TA#2, which does not include aPCell, the UE can autonomously determine which SCell in the group isused for a downlink timing reference (i.e. which node to obtain a TAvalue from). While the TA index value in the example of FIG. 5b islisted as an alphanumeric value, in practice the TA index value can be abinary string, such as a two or three bit binary string used todesignate the TA group.

The use of a specific TA index value to designate a TA group enables astate change of one serving cell to occur without impacting otherserving cells in the same TA group. A TA index value can be used touniquely identify a TA group when the member serving cells areconfigured for a TA group in a radio resource control (RRC) connectionreconfiguration. The RRC signaling may be dedicated or broadcast. Eachserving cell can be assigned to a particular TA group duringconfiguration of the node associated with the serving cell based on thenode's location in a cell. Thus, after configuration, the TA index valuewill not change for each serving cell. The TA index value can be definedin the 3GPP LTE specification, such as in Release 11 or Release 12.

FIG. 6 provides another example of carrier aggregation serving cells,comprising a PCell, and first and second SCells designated as SCell 1and SCell 2. SCell 2 includes a low power node that is illustrated as afrequency selective repeater in this example. The frequency selectiverepeater is used only for illustration purposes. Another type of lowpower node may also be used.

The actual TA value for a TA group can depend on where the UE is locatedwithin a cell. For example, when the UE is relatively close to thecenter of a cell, near the macro eNode B, and relatively far away fromthe frequency selective repeater (i.e. location 602), then the UEreceives transmission on SCell 2 from the macro eNode B only. Therefore,the UE only requires a single TA value for carrier aggregationoperation. However, when the UE is located near the frequency selectiverepeater (i.e. location 604), then the UE will receive transmissions inSCell 2 from the frequency selective repeater and the eNode B. Thus, twoseparate TAs can be used for carrier aggregation operations.

The eNode B may not have sufficient knowledge of UE location, prior tothe activation and use of the frequency selective repeater for uplinktransmission, to determine whether the frequency selective repeatershould be in a different TA group. In one embodiment, measurements andsignaling from the UE may be used to assist the eNode B in determiningan optimized mapping of each carrier to a selected TA to allow a minimumnumber of TAs to be configured and maintained.

In a typical environment, a relatively small number of TAs may need tobe configured and maintained. For example, a typical cell may only needbetween one and four different TA values based on the location of themacro eNode B and low power nodes within the cell, though this exampleis not intended to be limiting. Certain cell designs may implement alarge number of TAs when a large number of low power nodes aregeographically distributed throughout a cell.

Accordingly, in another embodiment, the eNode B can configure an SCellbased on a deployment configuration. When the node associated with theSCell is deployed, the node can be assigned to a particular TA group, aspreviously discussed. In the example of FIG. 6, the eNode B canconfigure a different TA group for SCell 2 since it includes thefrequency selective repeater that is disparately located relative to theeNode B. In this embodiment, the UE can always maintain two separate TAgroups. At certain locations, wherein the UE is relatively equaldistances from the eNode B and the frequency selective repeater, the TAvalues for the two separate TA groups may be about the same. In otherlocations, the TA values for the two separate TA groups will bedifferent. The TA groups will be maintained independent of the value ofeach TA.

In the example of FIG. 6, both SCell 1 and the PCell rely on one or moreeNode Bs or low power nodes that are collocated. Accordingly, SCell 1and the PCell can be assigned to the same TA group when they aredeployed. When the CA serving cells are assigned to a TA group atdeployment then the mapping of serving cells to TA groups is typicallynot changed based on the UE's location within a cell. In other words,the TA group configuration of serving cell/carrier to TA group mappingcan be eNode B specific.

When multiple TA groups are designated at deployment, each TA value canbe established and maintained independently. The initialization of a newTA relies on a random access procedure, as previously discussed. In oneembodiment, the initialization of a new TA may not be based on anadjustment that is relative to another previously established TA. Theindependence of each TA can reduce the risk of a UE communicating anunsynchronized uplink transmission to a node.

In one embodiment, a timing advance timer can be configured that isindependent for each TA instance. For example, the TA #1 can be a TAinstance for a first TA group that may correspond to a serving cell thatincludes a macro eNode B. TA #2 can be a TA instance for a second TAgroup that may correspond to a serving cell that includes a plurality ofrepeaters. The change of TA #2 can be much more significant than thechange of TA #1 when the position of the UE has changed. The eNode B canbe used to deploy different timing advance timers based on a selecteddeployment scenario. The eNode B can have full flexibility to determinewhich TA values should be adjusted, the time at which they are to beadjusted, the value by which the TA values will be adjusted, and theprocedure that will be used to adjust the TA values. Multiple TAs can beestablished and maintained independently, with a separate timing advancetimer used for each TA group.

The use of a specific TA index value to designate a TA group enables astate change of one serving cell to occur without impacting otherserving cells in the same TA group. A TA index value can be used touniquely identify a TA group when the member serving cells areconfigured for a TA group in RRC connection reconfiguration. Eachserving cell can be assigned to a particular TA group duringconfiguration of the node associated with the serving cell based on thenode's location in a cell. Thus, in one embodiment the TA index valuewill not change for each serving cell after it is configured. The TAindex value can be defined in the 3GPP LTE specification.

When only a single timing advance is used, as designated in 3GPP LTERelease 10, then a hybrid automatic retransmission request (HARQ) bufferfor the PCell and SCells(s) are flushed when the timing advance timerexpires. When multiple TA groups are formed, with potentially differenttypes of CA serving cells in each group, a different technique may beused.

In one embodiment, when a timing advance timer for a TA group that isassociated with a PCell expires (i.e. the TA for the PCell TA group islost), but the timing advance timer is unexpired for a second TA group(i.e. the TA is still valid), then the HARQ buffer for SCell(s) in thesecond TA group can also be flushed. The HARQ buffer for the second TAgroup comprising only SCells may be flushed since the supporting uplinkcontrol channel for the PCell will not be available to carry the HARQacknowledgement/negative acknowledgement (ACK/NACK) signals for theSCells. Alternatively, the HARQ buffers for the second TA group may bekept and not flushed.

In another embodiment, when the timing advance for a second TA groupthat is not associated with a PCell is lost (i.e. the timing advancetimer expires), but the timing advance for the TA group associated withthe PCell is still valid, there are three possible outcomes for the HARQbuffer for the SCells in the second TA group. First, the HARQ buffers ofthe second group can be flushed when the timing advance is lost. Second,the HARQ buffers of the second group may not be flushed when the timingadvance is lost. And third, the HARQ buffers of both the PCell TA groupand the second TA group may be flushed.

RACH Procedures for Multiple TAs

UE initiated random access channel (RACH) procedures are designated tobe carried by the PCell in the 3GPP LTE Release 8/9/10 specifications.The RACH can be used by an SCell to allow for adjustments of a TA forthe SCell. The need for an adjustment of a TA by an SCell is determinedby an eNode B. RACH procedures are triggered through a physical downlinkcontrol channel (PDCCH) order on a scheduling cell for the uplink forwhich a TA adjustment is needed. Since the RACH procedure for TAadjustment in SCells is always triggered by the eNode B, and the uplinkRACH transmissions are expected and directed by the eNode B, thetransmissions can be configured to use designated preambles to avoidpossible contention. Hence, contention based RACH consideration on anSCell is typically not necessary when there are multiple instances oftiming advances. Accordingly, UE initiated RACH transmissions andcontention based RACH on SCells is typically not needed to enforcemultiple TA support.

In the RACH procedure, several messages are communicated between the UEand the eNode B. A first message, referred to as message (msg) 0, is amessage from the eNode B to the UE asking the UE to perform an uplinktransmission that starts a timing advance. A second message, msg 1, issent from the UE to the eNode B that includes information that allowsthe eNode B to determine a TA adjustment, as outlined in the 3GPP LTERel. 8/9/10 specifications. A third message, msg 2, is sent from theeNode B to the UE that contains the amount of TA adjustment A Thephysical downlink control channel (PDCCH) for message (msg) 0 for anSCell can be sent on a scheduling carrier component, followed by msg 1on the uplink of the corresponding SCell. In one embodiment, thescheduling component carrier on the SCell carrying the PDCCH for msg 0can also be used for the PDCCH for msg 2. The SCell carrying thephysical downlink shared channel (PDSCH) for msg 2 can be indicated inthe corresponding physical downlink control channel.

The ability to send multiple RACH communications simultaneously may notbe needed since the RACH for multiple timing advances on differentSCells can be conducted on a per PDCCH order that is under the controlof the eNode B. If a UE loses a timing advance on a TA group associatedwith a PCell as well as on a second TA group that is not associated withthe PCell, the UE can first regain the TA on the PCell TA group and thentry to regain the TA of the second TA group sequentially. Determiningthe TA values for both TA groups can be more complex and is typicallynot considered to be critical to meet a performance requirement. If thetiming advance timers for each TA group expire independently then theneed for concurrent RACH transmissions for TA adjustments can be evenless likely. Accordingly, there is typically no need for multipleconcurrent RACH transmissions to obtain and/or maintain multiple TAs.

FIG. 7a provides an example of an SCell configuration procedure. In thisexample, the SCell is configured and then activated. The activated SCellstill does not have a TA value, so no UL transmissions can be made. APDCCH order can be used to trigger a RACH procedure to provide a TA andallow the activated cell to be used. The eNode B can assign uplinkgrants and the UE may start other uplink transmissions, such as the useof sounding reference signals if needed.

A different process is illustrated in FIG. 7b . The SCell is firstconfigured, but not activated. A RACH procedure is then performed on theconfigured, deactivated cell to form a deactivated cell having a TA. TheSCell is then activated to allow the SCell to be used.

In the process illustrated in FIG. 7a , the SCell is not immediatelyusable after activation until the RACH procedure is performed. In theprocess illustrated in FIG. 7b , the UE can obtain a new TA prior toactivation of the SCell. This allows the SCell to be used afteractivation. However, the UE must maintain the carrier aggregation for adeactivated cell. This maintenance can provide an undesired amount ofresources at both the UE and the eNode B. Accordingly, in oneembodiment, the TA for an SCell can be adjusted using a PDCCH orderfollowing the activation of the SCell. The TA can be adjusted using a TAgroup index value in the MAC CE.

In another example embodiment, the flow chart of FIG. 8 depicts a method800 for forming carrier aggregation timing advance groups in aheterogeneous network (HetNet). The method comprises assigning 810 atleast a first component carrier cell to one of a first timing advancegroup and a second timing advance group. An additional step involvesassigning 820 at least a second component carrier cell to one of thefirst timing advance group and the second timing advance group. Aseparate timing advance index value is selected 830 for each of thefirst and second timing advance groups. The timing advance index valueis used to refer to the timing advance group in signaling in the HetNet.

The method of FIG. 8 can further comprise assigning a component carriercell that is a PCell to the first timing advance group and using thePCell to obtain a timing advance value from a base station for the firsttiming advance group. The step of assigning the at least secondcomponent carrier cell can further comprise assigning at least onecomponent carrier cell that is a secondary cell (SCell) to the secondtiming advance group, and selecting one of the at least one SCells toobtain a timing advance value from a base station for the second timingadvance group.

Each of the at least first and the at least second component carriercells can be assigned to one of the first and second timing advancegroups based on a geographic location of each of the at least first andthe at least second component carrier cells relative to one another,wherein component carrier cells located within a selected distance ofeach other are assigned to a same timing advance group. A separatetiming advance timer can be maintained for each timing advance group.

In one embodiment, a HARQ buffer of the first timing advance group andthe second timing advance group can be flushed when a timing advance islost for a timing advance group associated with the PCell.

A scheduled time can be assigned for the SCell to perform a RACHprocedure to obtain a timing advance value from a base station in theHetNet for one of the first and second timing advance groups. Due to thescheduled time, the RACH procedure with the base station is notcontention based.

As previously discussed, the RACH procedure to obtain a timing advancevalue from the base station includes sending multiple messages between abase station and a mobile device. These messages are commonly referredto as message 0, 1 and 2. The component carrier cell that is configuredto carry a physical downlink control channel (PDCCH) for message 0 canalso be assigned to carry message 2. A timing advance value for thefirst timing advance group can be obtained at a non-concurrent time thana timing advance value is obtained for the second timing advance group.

In one embodiment, a timing advance value for one of the first and thesecond component carrier cells that is designated as an SCell in theHetNet can be adjusted using an order carried on a physical downlinkcontrol channel after an activation of the SCell using the timingadvance index value for the SCell's timing advance group that is locatedin a Medium Access Control (MAC) Control Element.

In another embodiment, an eNode B that is operable in a wireless networkand adapted for forming carrier aggregation timing advance groups in aHetNet is disclosed. The eNode B, such as the Macro eNode B depicted inFIG. 6, is configured to activate, at the eNode B, a component carrierthat is an SCell for a mobile device. The eNode B is further configuredto determine, at the eNode B, if the SCell is in a different timingadvance group than a primary cell (PCell) for the mobile device based ona predetermined timing advance index value received from the mobiledevice for the SCell. Alternatively, the SCell may be determined to bein a different timing advance group than the PCell based on a deploymentof a transmission station associated with the SCell. The SCell can becorrelated to a new or existing timing advance group using a timingadvance group index. The eNode B can send an order on a physicaldownlink control channel to the mobile device on the SCell for which thetiming advance adjustment is needed when the SCell's timing advanceindex value is different than a timing advance index value for thePCell. The eNode B can send the order to the SCell after the SCell isactivated, as previously discussed. The order can be sent using thetiming advance index value for the SCell's timing advance group that islocated in a Medium Access Control (MAC) Control Element. The eNode Bcan maintain a separate timing advance timer for each timing advancegroup.

FIG. 9 provides an example illustration of a mobile device, such as auser equipment (UE), a mobile station (MS), a mobile wireless device, amobile communication device, a tablet, a handset, or other type ofmobile wireless device. The mobile device can include one or moreantennas configured to communicate with a base station (BS), an evolvedNode B (eNB), or other type of wireless wide area network (WWAN) accesspoint. While two antennas are shown, the mobile device may have betweenone and four or more antennas. The mobile device can be configured tocommunicate using at least one wireless communication standard includingThird Generation Partnership Project Long Term Evolution (3GPP LTE),Worldwide interoperability for Microwave Access (WiMAX), High SpeedPacket Access (HSPA), Bluetooth, WiFi, or other wireless standards. Themobile device can communicate using separate antennas for each wirelesscommunication standard or shared antennas for multiple wirelesscommunication standards. The mobile device can communicate in a wirelesslocal area network (WLAN), a wireless personal area network (WPAN),and/or a wireless wide area network (WWAN).

FIG. 9 also provides an illustration of a microphone and one or morespeakers that can be used for audio input and output from the mobiledevice. The display screen may be a liquid crystal display (LCD) screen,or other type of display screen such as an organic light emitting diode(OLED) display. The display screen can be configured as a touch screen.The touch screen may use capacitive, resistive, or another type of touchscreen technology. An application processor and a graphics processor canbe coupled to internal memory to provide processing and displaycapabilities. A non-volatile memory port can also be used to providedata input/output options to a user. The non-volatile memory port mayalso be used to expand the memory capabilities of the mobile device. Akeyboard may be integrated with the mobile device or wirelesslyconnected to the mobile device to provide additional user input. Avirtual keyboard may also be provided using the touch screen.

It should be understood that many of the functional units described inthis specification have been labeled as modules, in order to moreparticularly emphasize their implementation independence. For example, amodule may be implemented as a hardware circuit comprising custom VLSIcircuits or gate arrays, off-the-shelf semiconductors such as logicchips, transistors, or other discrete components. A module may also beimplemented in programmable hardware devices such as field programmablegate arrays, programmable array logic, programmable logic devices or thelike.

Modules may also be implemented in software for execution by varioustypes of processors. An identified module of executable code may, forinstance, comprise one or more physical or logical blocks of computerinstructions, which may, for instance, be organized as an object,procedure, or function. Nevertheless, the executables of an identifiedmodule need not be physically located together, but may comprisedisparate instructions stored in different locations which, when joinedlogically together, comprise the module and achieve the stated purposefor the module.

Indeed, a module of executable code may be a single instruction, or manyinstructions, and may even be distributed over several different codesegments, among different programs, and across several memory devices.Similarly, operational data may be identified and illustrated hereinwithin modules, and may be embodied in any suitable form and organizedwithin any suitable type of data structure. The operational data may becollected as a single data set, or may be distributed over differentlocations including over different storage devices, and may exist, atleast partially, merely as electronic signals on a system or network.The modules may be passive or active, including agents operable toperform desired functions.

Various techniques, or certain aspects or portions thereof, may take theform of program code (i.e., instructions) embodied in tangible media,such as floppy diskettes, CD-ROMs, hard drives, or any othermachine-readable storage medium wherein, when the program code is loadedinto and executed by a machine, such as a computer, the machine becomesan apparatus for practicing the various techniques. In the case ofprogram code execution on programmable computers, the computing devicemay include a processor, a storage medium readable by the processor(including volatile and non-volatile memory and/or storage elements), atleast one input device, and at least one output device. One or moreprograms that may implement or utilize the various techniques describedherein may use an application programming interface (API), reusablecontrols, and the like. Such programs may be implemented in a high levelprocedural or object oriented programming language to communicate with acomputer system. However, the program(s) may be implemented in assemblyor machine language, if desired. In any case, the language may be acompiled or interpreted language, and combined with hardwareimplementations.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, appearancesof the phrases “in one embodiment” or “in an embodiment” in variousplaces throughout this specification are not necessarily all referringto the same embodiment.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary. In addition, various embodiments and example of the presentinvention may be referred to herein along with alternatives for thevarious components thereof. It is understood that such embodiments,examples, and alternatives are not to be construed as defectoequivalents of one another, but are to be considered as separate andautonomous representations of the present invention.

Furthermore, the described features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided, such asexamples of materials, fasteners, sizes, lengths, widths, shapes, etc.,to provide a thorough understanding of embodiments of the invention. Oneskilled in the relevant art will recognize, however, that the inventioncan be practiced without one or more of the specific details, or withother methods, components, materials, etc. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the invention.

While the forgoing examples are illustrative of the principles of thepresent invention in one or more particular applications, it will beapparent to those of ordinary skill in the art that numerousmodifications in form, usage and details of implementation can be madewithout the exercise of inventive faculty, and without departing fromthe principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims setforth below.

What is claimed is:
 1. An apparatus of an eNodeB operable to maintaintiming advance groups (TAGs) in a heterogeneous network (HetNet), theapparatus comprising one or more processors and memory configured to:form, at the eNodeB, a timing advance group (TAG) for one or moreserving cells when a same timing advance applies to the one or moreserving cells; map, at the eNodeB, each of the one or more serving cellsto the TAG using radio resource control (RRC) signaling from the eNodeB;and assign, from the eNodeB, a timing advance group identifier (TAG ID)to the one or more serving cells mapped to the TAG, wherein a separatetiming advance timer is maintained at a user equipment (UE) for each TAGfor a selected period of time.
 2. The apparatus of claim 1, wherein theone or more processors and memory are further configured to: instruct auser equipment (UE) to select a serving cell from the TAG to use as atiming reference at the UE for the one or more serving cells in the TAG.3. The apparatus of claim 1, wherein the TAG ID has a field length of 2bits.
 4. The apparatus of claim 1, wherein the TAG ID is included in atiming advance command medium access control (MAC) control element (CE).5. The apparatus of claim 1, wherein the eNodeB is configured tocommunicate with a user equipment (UE), wherein the UE includes anantenna, a touch sensitive display screen, a speaker, a microphone, agraphics processor, an application processor, an internal memory, anon-volatile memory port, and combinations thereof.
 6. An apparatus of auser equipment (UE) operable to flush one or more hybrid automaticretransmission request (HARM) buffers, the apparatus comprising one ormore processors and memory configured to: identify, at the UE, a timingadvance group (TAG) for one or more serving cells; determine, at the UE,when a timing advance timer for the TAG expires; and flush, at the UE,all HARQ buffers for all serving cells when the timing advance timer forthe TAG expires.
 7. The apparatus of claim 6, wherein a TAG ID isassigned to the one or more serving cells mapped to the TAG, wherein theTAG ID has a field length of 2 bits.
 8. The apparatus of claim 6,wherein a TAG ID is assigned to the one or more serving cells mapped tothe TAG, wherein the TAG ID is included in a timing advance commandmedium access control (MAC) control element (CE).
 9. The apparatus ofclaim 6, wherein the UE is configured to maintain a separate timingadvance timer for each TAG for a selected period of time.
 10. At leastone non-transitory machine readable storage medium having instructionsembodied thereon for maintaining timing advance groups (TAGs) at aneNodeB, the instructions when executed by one or more processors causethe one or more processors perform the following: forming, using atleast one processor of the eNodeB, a timing advance group (TAG) for oneor more serving cells when a same timing advance applies to the one ormore serving cells; mapping, using the at least one processor of theeNodeB, each of the one or more serving cells to the TAG using radioresource control (RRC) signaling from the eNodeB; assigning, using theat least one processor of the eNodeB, a timing advance group identifier(TAG ID) to the one or more serving cells mapped to the TAG; andconfiguring a user equipment (UE) to maintain a separate timing advancetimer for each TAG for a selected period of time.
 11. The at least onenon-transitory machine readable storage medium of claim 10, furthercomprising instructions when executed perform the following: instructinga user equipment (UE) to select a serving cell from the TAG to use as atiming reference at the UE for the one or more serving cells in the TAG.12. The at least one non-transitory machine readable storage medium ofclaim 10, wherein the TAG ID has a field length of 2 bits.
 13. The atleast one non-transitory machine readable storage medium of claim 10,wherein the TAG ID is included in a timing advance command medium accesscontrol (MAC) control element (CE).
 14. The at least one non-transitorymachine readable storage medium of claim 10, wherein the UE includes anantenna, a touch sensitive display screen, a speaker, a microphone, agraphics processor, an application processor, an internal memory, anon-volatile memory port, and combinations thereof.
 15. At least onenon-transitory machine readable storage medium having instructionsembodied thereon for flushing one or more hybrid automaticretransmission request (HARQ) buffers at a user equipment (UE), theinstructions when executed by one or more processors cause the one ormore processors perform the following: identifying, using one or moreprocessors of the UE, a timing advance group (TAG) for one or moreserving cells; determining, using the one or more processors of the UE,when a timing advance timer for the TAG expires; and flushing, using theone or more processors of the UE, all HARQ buffers for all serving cellswhen the timing advance timer for the TAG expires.
 16. The at least onenon-transitory machine readable storage medium of claim 15, wherein aTAG ID is assigned to the one or more serving cells mapped to the TAG,wherein the TAG ID has a field length of 2 bits.
 17. The at least onenon-transitory machine readable storage medium of claim 15, wherein aTAG ID is assigned to the one or more serving cells mapped to the TAG,wherein the TAG ID is included in a timing advance command medium accesscontrol (MAC) control element (CE).
 18. The at least one non-transitorymachine readable storage medium of claim 15, further comprisinginstructions which when executed perform the following: maintaining aseparate timing advance timer at the UE for each TAG for a selectedperiod of time.
 19. The at least one non-transitory machine readablestorage medium of claim 15, wherein the TAG is formed for the one ormore serving cells when a same timing advance applies to the one or moreserving cells.
 20. The at least one non-transitory machine readablestorage medium of claim 15, wherein the UE includes an antenna, a touchsensitive display screen, a speaker, a microphone, a graphics processor,an application processor, an internal memory, a non-volatile memoryport, and combinations thereof.